The clinical failure of alkylating agents such as cyclophosphamide (CY) in multiple myeloma has been attributed to the emergence of drug resistant tumor cells. In order to understand the biology and mechanism of this acquired drug resistance, we have developed a CY-resistant (CY-R) tumor line from its drug-sensitive parent, LPC-1 plasmacytoma. To achieve our objectives, we will further characterize our LPC-1/CY-R tumor line with respect to its: cross reactivity to other drugs; DNA distribution; surface membrane properties; antigenicity; tumorigenicity; and growth characteristics. Using a similar subcurative therapeutic protocol, we will attempt to induce CY resistance in other mouse plasmacytomas and compare the properties of these cell lines to our established LPC-1/CY-R. We will develop in vitro assays to predict drug resistance based on cellular metabolic activities, i.e., DNA and protein synthesis during short-term culture. In certain cases, where toxic doses of drug will be used, tumor cells will be rescued to monitor their survival/tumorigenicity after drug treatment. We will analyze the biochemical-molecular determinants that could account for CY resistance such as the role of membrane receptors, intracellular transport, DNA repair mechanisms and polyploidy. Drug-induced DNA crosslinks will be measured and removal/repair of these damaged sites will be studied. We will analyze the stability and the mode of inheritance of the alkylating agent resistance by cell hybridization techniques. From our work with this animal model, we have developed experimental approaches that will be useful for studying the development of resistance to alkylating agents in human multiple myeloma (MM). Our experience with this mouse myeloma may also provide clues for more effective alternative treatment and scheduling in our myeloma patients.